Saturation of the ion-hammering effect for large non-hydrostatic capillarity stresses in colloidal silica nanoparticles

Abstract

We investigate the role of capillarity stresses on the ion-hammering phenomenon when sub-micrometer colloidal particles are considered. To this end, nearly monodisperse, chemically synthesized silica (SiO2) colloids (100, 300 and 600nm) were irradiated at room temperature (300K) with 4MeV Au ions for fluences up to Φ = 1.8 × 1016cm-2. It has been taken for granted that the transverse dimension of an ion-deformable amorphous material grows exponentially with the irradiation fluence, L(φ) = L(0)exp[A0Φ]. Here, we show that for sub-micrometer particles the irradiation-induced deformation saturates for larger fluences, const. The saturation fluence depends on the initial dimension of the colloidal nanoparticles: the smaller the dimension of the colloids, the lower the saturation fluence. Experimental data are successfully accounted for by having recourse to a phenomenological model first developed by Klaumünzer and further elaborated by van Dillen. We also estimate the evolution with fluence of the principal stresses inside the particles, σ11(φ) = σ22(φ) and σ33(φ), and we show that they evolve toward a steady-state value following a sigmoidal-like behavior. Furthermore, when stresses induced by the surface curvature become non-negligible the approximation often made that the deformation strain rate, A0 = dL/L dΦ, remains constant upon irradiation is no longer valid. We show that A0 evolves with the irradiation fluence, e.g., A0 → A(φ) and we relate this behavior to the evolution of the stresses upon irradiation. Finally, this work allows us to define the limits of the ion-hammering effect when the non-hydrostatic capillarity stresses become important. Show more